Al2O3 H2O Research Articles

Synthesis and characterization of hydrogarnet Ca3(AlxFe1 − x)2(SiO4)y(OH)4(3 − y)

C3AH6 is a stable phase in the CaO–Al2O3–H2O system at temperatures 20°C and above. The presence of SiO2 results in the formation of C3AH6 and C–S–H phases at room temperature. At 110°C crystalline C3ASyH2(3−y) phases form. Two solid solutions: C3AH6–C3AS0.41H5.18 and C3AS0.84H4.32–C3AS3 are found with log Ks0=−20.50, −25.35, −26.70 and −39.7 at 20°C, respectively. In the CaO–Fe2O3–H2O system, only traces of C3FH6 and C4FH13 phases are formed due to the high stability of FH phase. The presence of silica leads between 20 and 110°C to the formation of C3FS0.84H4.32 and C3FS1.34H3.32 phases with log Ks0=−32.50 and −34.20 at 25°C. No significant solid solution formation occurred between C3AH6 and C3FH6 end members, but between C3AS0.84H4.32 and C3FS0.84H4.32 solid solution formation is observed. The determined solubility products indicate that C3FS0.84H4.32 is the most stable iron-containing phase in hydrated Portland cements.

Mixed-convection flow of Al2O3–H2O nanofluid in a channel partially filled with porous metal foam: Experimental and numerical study

Mixed-convection flow of nanofluids inside a vertical rectangular channel partially filled with open-cell metal foam and subject to a constant wall-heat flux was investigated experimentally and numerically. Al2O3–water nanofluids with different concentrations were prepared and their stability was examined using UV–Vis spectroscopy. Dynamic light scattering method was used to determine particle size distribution of the nanofluid feedstock. The outlet temperature and pressure drop were measured for different nanofluid flow rates (i.e., Reynolds number values). In the numerical section, a two-dimensional volume-averaged form of the governing equations was used. The velocity and temperature profiles of nanofluid were obtained using finite difference method. Effects of nanoparticles Brownian and thermophoretic diffusions were taken into account in the governing equations and the local thermal equilibrium assumption was made for the solid and fluid phases. The simulation results were validated against those obtained experimentally and acceptable agreement was found.

Numerical investigation of trapezoidal grooved microchannel heat sink using nanofluids

A numerical investigation is performed to study the thermal and flow fields in a trapezoidal grooved microchannel heat sink (TGMCHS) using nanofluids. The governing and energy equations are solved using the finite volume method. The influence of the geometrical parameters such as the width, depth and pitch of the groove on the thermal performance of TGMCHS was examined. The effects of different nanoparticle types, volume fraction, particle diameter and base fluid at different Reynolds numbers are also studied. It is found that the increment of the maximum width ‘a’ and reduction of the minimum width ‘b’ of the trapezoidal groove gives the maximum thermal performance and this implies that the triangular shape would be favorable compared to rectangular shape MCHS. It is inferred that Al2O3–H2O had the highest thermal performance with 0.04 volume fraction and 25nm particle diameter.

Experimental investigation on heat transfer enhancement due to Al2O3–water nanofluid using impingement of round jet on circular disk

An experimental study was performed to investigate the convective heat transfer coefficient (HTC) of Al2O3–H2O nanofluid using impingement of a fluid jet on a flat circular disk. Nanofluid enhanced the measured HTC values, as compared with the HTC values when using water. Nanofluids, in this case, were prepared with different concentration of nanoparticles in water. The pH of the fluid was adjusted to a desirable value and Sodium Dodecyl Benzene Sulfonate (SDBS) was added to the fluid as a dispersant. These composite fluids were shown to be stable and during experiments no sedimentation was observed. To investigate the effects of the Reynolds number as well as nanoparticle concentration on the local and average HTCs, the Reynolds number was varied in the range of 4200–8200 and the nanoparticle concentration was varied from 0.0198 to 0.0757 wt%. The results showed that, although the nanofluids increased HTCs, the maximum enhancement would correspond to the nanofluid with nanoparticle concentration of 0.0597 wt% and adding more nanoparticles did not prove to be beneficial. In fact the nanoparticle concentration of 0.0757 wt% demonstrated the lowest enhancement in HTC. The maximum enhancement of the average nanofluid HTC in comparison with water is about 50% for Reynolds number of 4200. The average HTC of nanofluids was also remained constant with the increase of Reynolds number due to nanoconvection.

Cost Effective Deposition of Aluminium Oxide Layers

Al2O3 surface-layers were deposited on Al substrates by thermal evaporation technique. Samples were treated for different (1 h, 2 h, 3 h, 4 h and 5 h) treatment time in open air environment by keeping the temperature (550oC) of the evaporator plate constant. XRD patterns revealed the emergence of Al2O3 H2O (111), Al (OH)3 (214) and Al2O3 (20 6) planes. Crystallinity of the above mentioned phases was attributed with treatment time. However, minimum treatment time to break oxygen hydrogen bonds and the formation of Al2O3 plane was 5 h. Crystallite size and compressive stress found in Al2O3 (2 0 6) plane were 14.31 nm 0.53 GPa respectively. SEM microstructure features revealed the formation of rounded grains, irregular patches and rods. AFM analysis exhibited the formation of dome shapes microstructures. The grain size and surface roughness were increased from 1 ?m to 2.5 ?m and from 35 nm to 115 nm respectively. This variation in surface roughness and grain sizes was associated with treatment time.

Stability in the system CaO–Al2O3–H2O

The solubility of AH3, CAH10, C2AH7.5, and C3AH6 was determined experimentally at 7 to 40°C and up to 570days. During the reaction of CA, at 20°C and above initially C2AH7.5 formed which was unstable in the long-term. The solubility products calculated indicate that the solubilities of CAH10, C2AH7.5 and C4AH19 increase with temperature while the solubility of C3AH6 decreases. Thus at temperatures above 20°C, C3AH6 is stable, while at lower temperature also CAH10 and C4AH19 are stable, depending on the C/A ratio.At early hydration times, CAH10 can be stable initially at 30°C and above, as the formation of amorphous AH3 stabilises CAH10 with respect to C3AH6+2AH3. With time, as the solubility AH3 decreases due to the formation of microcrystalline AH3, CAH10 becomes unstable at 20°C and above.

Solubility of the System KOH–K2CrO4–Al2O3–H2O at 150 °C in a High Alkali Concentrated Region

The phase equilibria for the system KOH–K2CrO4–Al2O3–H2O and its subsystems at 150 °C in a high alkali concentrated region were investigated. In the concentrated alkali region of the system and its subsystem KOH–Al2O3–H2O, the equilibrium solid-phase K2O·Al2O3·2H2O was found. This is different from the system KOH–Al2O3–H2O at low temperature from which the equilibrium solid-phase K2O·Al2O3·3H2O was discovered. The salting-out effect of KOH and potassium aluminate to K2CrO4 is strong. These findings can provide a significant and precious database for the production of K2CrO4 and the removal of alumina from the concentrated alkali solution that is produced in the chromate cleaner production process.

Trace element distribution and Cr(VI) speciation in Ca-HCO3 and Mg-HCO3 spring waters from the northern sector of the Pollino massif, southern Italy

Weathering of outcrops of ultramafic rocks (remnants of ancient oceanic crust) is a source of biologically toxic trace elements, particularly first row transition elements. The Cr and Ni concentrations of serpentinite and metabasite outcrops in the northern sector of the Pollino massif (Lucanian Apennines, southern Italy) are hundreds of orders of magnitude higher than those of the upper continental crust. In this region, exposed intermediate to lower crustal rocks are significantly enriched in Ni, Cr, and V relative to the average upper continental crust. We evaluate the levels and distributions of trace elements of environmental concern, including Cr (as total dissolved Cr and Cr(VI)), V, Mn, Fe, Ni, Cu, Zn, As, Pb, and U, in spring waters from the northern sector of the Pollino massif.The major solutes in the spring waters from this region are Mg-HCO3 and Ca-HCO3. The Mg-HCO3 type waters are produced mainly through the interaction of meteoric waters with serpentinites, whereas the Ca-HCO3 type waters are produced through the interaction of meteoric waters with Ca-rich rocks (i.e., carbonate rocks, calc-schists, and metabasites). Thermodynamic evaluation indicates that in the MgO–SiO2–Al2O3–H2O system, waters flowing in serpentinites fall in the kaolinite field, close to the kaolinite–Mg-vermiculite phase boundary. This result arises because kaolinite is a relatively early reaction product, which is consumed to produce Mg-vermiculite and further Mg-saponite. In the CaO–SiO2–Al2O3–H2O system, Ca-HCO3 type waters fall either in the field of gibbsite or kaolinite, depending on dissolved silica.Chromium (VI) contamination associated with local mineralogy and with maximum admissible concentration >5μgL−1 was observed for nine springs (both Mg-HCO3 and Ca-HCO3 type waters). The Cr(VI)-rich Ca-HCO3 springs are not located in serpentinites. However, some of these waters likely acquire their high Cr levels from interacting with serpentinite clasts, as in the case of springs flowing through conglomerates. In addition, Cr(VI) contamination is not limited to waters interacting with serpentinites or serpentinite clasts, because in one case weathering of garnet-rich gneiss is responsible for the release of significant amounts of Cr(VI) in solution.Finally, studies are needed to address the potential health risks associated with the observed high concentrations of Cr(VI) in waters from the Pollino massif area. A mode-of-action analysis is needed to evaluate adverse health risks associated with exposure to Cr(VI) in drinking water, especially as Cr contamination is not limited to springs flowing through serpentinites.

Thermal Physics and Critical Heat Flux Characteristics of Al2O3–H2O Nanofluids

This study investigates the influence of the thermal physics of nanofluids on the critical heat flux (CHF) of nanofluids. Thermal physics tests of nanoparticle concentrations ranged from 0 to 1 g/L. Pool boiling experiments were performed using electrically heated NiCr metal wire under atmospheric pressure. The results show that there was no obvious change for viscosity and a maximum enhancement of about 5 to 7% for thermal conductivity and surface tension with the addition of nanoparticles into pure water. Consistently with other nanofluid studies, this study found that a significant enhancement in CHF could be achieved at modest nanoparticle concentrations (<0.1 g/L by Al2O3 nanoparticle concentration). Compared to the CHF of pure water, an enhancement of 113% over that of nanofluids was found. Scanning electron microscope photos showed there was a nanoparticle layer formed on the heating surface for nanofluid boiling. The bubble growth was photographed by a camera. The coating layer makes the nucleation of vapor bubbles easily formed. Thus, the addition of nanoparticles has active effects on the CHF.

Dispersion behavior and thermal conductivity characteristics of Al2O3–H2O nanofluids

Abstract Nanofluid is a kind of new engineering material consisting of solid nanoparticles with sizes typically of 1–100 nm suspended in base fluids. In this study, Al2O3–H2O nanofluids were synthesized, their dispersion behaviors and thermal conductivity in water were investigated under different pH values and different sodium dodecylbenzenesulfonate (SDBS) concentration. The sedimentation kinetics was determined by examining the absorbency of particle in solution. The zeta potential and particle size of the particles were measured and the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory was used to calculate attractive and repulsive potentials. The thermal conductivity was measured by a hot disk thermal constants analyser. The results showed that the stability and thermal conductivity enhancements of Al2O3–H2O nanofluids are highly dependent on pH values and different SDBS dispersant concentration of nano-suspensions, with an optimal pH value and SDBS concentration for the best dispersion behavior and the highest thermal conductivity. The absolute value of zeta potential and the absorbency of nano-Al2O3 suspensions with SDBS dispersant are higher at pH 8.0. The calculated DLVO interparticle interaction potentials verified the experimental results of the pH effect on the stability behavior. The Al2O3–H2O nanofluids with an ounce of Al2O3 have noticeably higher thermal conductivity than the base fluid without nanoparticles, for Al2O3 nanoparticles at a weight fraction of 0.0015 (0.15 wt%), thermal conductivity was enhanced by up to 10.1%.

The application of focused microwave irradiation coupled with freeze drying to investigate the reaction of MgO and Al2O3 slurries in the formation of layered double hydroxides

Focused microwave irradiation (MI) and freeze drying (FD) techniques have been used to study the generation of layered double hydroxides prepared from MgO–Al2O3–H2O systems. Reactions were undertaken at temperatures of between 100 and 180 °C in order to study the formation of the 3R1 and 3R2 polytypes, respectively. MI was found to enhance the rate of formation of both polytypes. FD provided an effective means of quenching the reaction, enabling effective ex situ analysis at intermediate stages. The phase selectivity of the reaction was shown to vary with temperature, promoting the formation of an impurity Mg(OH)2 at elevated temperatures.

Experimental Model of Temperature-Driven Nanofluid

This paper presents a systematic experimental method of studying the heat transfer behavior of buoyancy-driven nanofluids. The presence of nanoparticles in buoyancy-driven flows affects the thermophysical properties of the fluid and consequently alters the rate of heat transfer. The focus of this paper is to estimate the range of volume fractions that results in maximum thermal enhancement and the impact of volume fraction on Nusselt number. The test cell for the nanofluid is a two-dimensional rectangular enclosure with differentially heated vertical walls and adiabatic horizontal walls filled with 27 nm Al2O3–H2O nanofluid. Simulations were performed to measure the transient and steady-state thermal response of nanofluid to imposed isothermal condition. The volume fraction is varied between 0% and 8%. It is observed that the trend of the temporal and spatial evolution of temperature profile for the nanofluid mimics that of the carrier fluid. Hence, the behaviors of both fluids are similar. Results shows that for small volume fraction, 0.2⩽ϕ⩽2% the presence of the nanoparticles does not impede the free convective heat transfer, rather it augments the rate of heat transfer. However, for large volume fraction ϕ&gt;2%, the convective heat transfer coefficient declines due to reduction in the Rayleigh number caused by increase in kinematic viscosity. Also, an empirical correlation for Nuϕ as a function of ϕ and Ra has been developed, and it is observed that the nanoparticle enhances heat transfer rate even at a small volume fraction.

Templating of high-silica zeolites by tetrahydrofuran in the Na2O – SiO2 – Al2O3 – H2O system

The spontaneous crystallization of high-silica MOR, FER, MFI, MTN zeolites was investigated in the reactant system tetrahydrofuran (THF)–Na2O–SiO2–Al2O3–H2O in the temperature range 180–230°C. 13C CP MAS NMR spectra, TG/DTG/DTA and energy dispersive X-ray (EDX) analysis were used to characterize the molecules of THF trapped in the channels or the cages of the as-synthesized zeolites. The regular patterns and the distinct shift of the resonance peaks for THF in 13C MAS NMR spectra, and the higher temperatures for THF escaping from the as-synthesized zeolites confirm that THF interacts strongly with the framework of the zeolites, playing the role of a template. The mechanism of the interaction between the framework and THF is also discussed.

Dehydroxylation of Aluminum (Oxo)Hydroxides Using Infrared Emission Spectroscopy. Part II: Boehmite

The dehydroxylation of boehmite has been studied by the application of infrared emission spectroscopy over the 200 to 750 °C temperature range. The dehydroxylation is followed by the loss of intensity of the hydroxyl stretching frequencies observed at 3478, 3319, and 3129 cm−1 and by the loss of intensity of the hydroxyl deformation modes at 1140 and 1057 cm−1. Dehydroxylation starts at 250 °C and is complete by 450 °C. No difference was found between the synthetic and natural boehmite dehydroxylation. The hydroxyl stretching frequencies show a pronounced blue shift, while the hydroxyl deformation modes show a pronounced red shift. Infrared absorption bands were observed at 3413, 3283, and 3096 cm−1 for the hydroxyl stretching frequencies and at 1161 and 1071 cm−1 for the hydroxyl deformation frequencies. Low-frequency infrared absorption bands are observed at 749, 635, and 542 cm−1 and infrared emission bands at 811, 716, 611, and 456 cm−1. The infrared emission low-frequency bands moved to higher frequencies upon thermal treatment. Spectral changes in the low-frequency bands confirm that dehydroxylation commenced at 250°C. Infrared emission spectroscopy allows the phase changes of the Al2O3–H2O alumina system to be studied in situ at the elevated temperatures.

Hydrothermal synthesis and characterization of diaspore,?-Al2O3 � H2O

An acicular single crystal of diaspore was synthesized under the conditions of 1 N NaOH, 450 ° C and 1200 kg cm−2 and characterized by means of X-ray diffraction, scanning electron microscopy, electron diffraction and infrared spectroscopy. The reactivity of three kinds of natural ores containing diaspore which were used as a seed crystal for synthesis of diaspore was also compared.

Crystallization field of zeolite T at 100 °C for a SiO2/Al2O3 ratio of 28 and crystallization sequences in the Na2O–K2O–SiO2–Al2O3–H2O system

A crystallization field of zeolite T has been found at n= 28 which differs in area and shape from those with lower values of n. Crystallization has been found to be very sensitive to changes in the ratio of OH to SiO2 in the reaction mixture. Crystallization sequences of zeolite phases, depending on the composition of the reaction mixture, have been plotted and the disproportionation phenomenon has been observed.

跡津川断層に伴う断層内物質 ＩＩ 粒度別鉱物組成および化学組成

Mineralogical and geochemical studies carried out on intrafault materials collected at two outcrops of the Atotsugawa fault of Central Japan, which had been described in detail in the previous paper. A sample of the intrafault materials was divided into four fractions of 2μ>, 2-74μ 74-250μ and 250μ< by their grain size. Mineralogy and geochemical compositions were examined in each fraction of the sample. The three fractions of 2μ< have almost similar mineralogy and geochemical compositions. Mineralogically, the 2μ>fraction is including more amount of montmorillonite, illite and chlorite and on the contrary less amount of quartz, feldspar and calcite than the other three fractions. The geochemical compositions of the 2μ< fraction is rich in Al2O3, MgO, K2O and total H2O and poor in SiO2, CaO, Na2O and CO2, comparing with those of the other three fractions. It is disclosed that the mineralogy, geochemical compositions and grain size of the intrafault materials have close relationship one another and should be related to the formation process of the materials and the degree of their weathering or alteration.

Phillipsite‐type synthetic zeolite with high silica contents and accompanying phases

AbstractA zeolite of P type with a molar ratio SiO2 : Al2O3 of about 6 was obtained on laboratory and on enlarged scale, by synthesis carried out at 100°C in Na2OK2OSiO2Al2O3H2O system, without complexing agents. It was found that the products depend not only on the chemical composition of hydrogel but also on the kinetic factors such as: the material of the reactor wall, the amount of substrates taken for crystallization and stiring. It was found that the stability of zeolites increases in the order: L &lt; T &lt; Ch &lt; P. The factors accelerating crystallization led to the more stable zeolites as products. The paper shows difficulties in implementing the laboratory results into an industrial production.

Action of water and lime solutions on anhydrous calcium aluminates at 5°c

AbstractSpecimens of CA, CA2* and Secar 250 (a mixture of these two compounds together with corundum) were treated with water or lime solutions in dilute suspension at 5°. The results confirm the reactivity of CA with water or lime solutions and show that CA2 also reacts, though more slowly, either alone or in the presence of CA. They also confirm some of the solubility curves already established for the CaOAl2O3H2O system at 5°, and help especially to locate the triple point C4AH19C2AH8 solution.

433. The system CaO–Al2O3–H2O at 5°

433. The system CaO–Al₂O₃–H₂O at 5°